WebApp version 3.4.16.1544+881 and below, calendar issue with autorefresh

To simulate:
Make a calendar item and change the category for example into red save and reedit the item again.
Go to category and wait for the blink of the page (Autorefresh) then try to unset the category red.
This does not work, setting a other item in this window is no problem.

First step is to create a item in the calendar, with some categories.
Save the item then right click the item and go to the change the category window.
Don’t click anything until the refresh blink, after this blink you cannot deselect the category set in the first step.